Fluid pressure amplifier



Nov. 24, 1970 J. 1'. ELLIS, JR 3,541,792

FLUID PRESSURE AMPLIFIER Filed Fb. 19, 1968 V 2 Sheets-Sheet 1 /F=O= 1L4 l -35 1 Nov. 24, 1970 J. T. ELLIS, JR

FLUID PRESSURE AMPLIFIER 2 Sheets-Sheet 2 Filed Feb. 19, 1968 United States Patent 3,541,792 FLUID PRESSURE AMPLIFIER John T. Ellis, In, Chicago, Ill., assignor to Ellis Engineering, Inc., Chicago, Ill., a corporation of Illinois Filed Feb. 19, 1968, Ser. No. 706,487 Int. Cl. F15b 7/00; F16j 15/18 US. Cl. fill-54.5 12 Claims ABSTMCT OF THE DISCLOSURE This fluid pressure amplifier utilizes air at low pressure to deliver hydraulic fluid at a high pressure. The amplifier includes a relatively large diameter air cylinder, a relatively small diameter hydraulic fluid cylinder, and a piston reciprocally mounted in the air cylinder having a rod which is formed integral with the piston in the hydraulic cylinder. A reservoir is mounted concentric with the hydraulic cylinder, and a hydraulic fluid flow path is provided to deliver hydraulic fluid from the reservoir to the hydraulic cylinder to replenish leaked hydraulic fluid.

BACKGROUND OF THE INVENTION It is well recognized in machine shops that hydraulically operated work holding devices and other such pieces of equipment may be utilized to increase the efiiciency of the overall operation of a machine shop. Many machineshops, and especially, smaller machine shops, do not have the necessary facilities for providing high pressure hydraulic fluid at a variety of locations so that work holding devices and other such pieces of equipment may not be quickly and readily installed and used in a plurality of positions. Customarily, machine shops have available air compressors, and compressed air lines are usually positioned at convenient locations. Compressed air, as such, is used for numerous applications, from cleaning metal chips from Work pieces to operating low pressure devices.

Recognizing the fact that most machine shops have compressed air readily available, and it is desirable to provide hydraulic fluid at a high pressure for specific applications, many conversion devices have been developed wherein the low pressure air is utilized to develop a high pressure hydraulic fluid. Many of these devices have a problem in that the hydraulic devices are customarily used in repetitive activities, and seals, in many instances, are not perfect so that there is a slight leakage of hydraulic fluid. Thereby, some of the hydraulic fluid is lost, which creates inefficiencies in the operation of the hydraulic device. In some instances, the stroke of the device is diminished for lack of hydraulic fluid. A more common problem is that as the hydraulic device is being used, at one portion of the stroke there is insuflicient hydraulic fluid to fill the space thereby creating a partial vacuum which tends to suckair into the system, thereby making the system compressible and seriously limiting the force which may be generated by the hydraulic device.

SUMMARY OF THE INVENTION The instant fluid amplifier includes a relatively large air cylinder with a piston reciprocally mounted in the cylinder. The cylinder is a double acting cylinder so that there is positive displacement of the piston in both directions. A rod is connected to the cylinder and the rod extends into a small diameter, high pressure hydraulic cylinder. A high pressure piston is formed integral with the rod, which high pressure piston is reciprocally mounted in the hydraulic cylinder. A hydraulic fluid reservoir surrounds the hydaulic cylinder, and a flow path is provided from the reservoir to the hydraulic cylinder with a valve in the flow path to control the flow of hydraulic fluid from the reservoir to the hydraulic cylinder ice to replenish leaked hydraulic fluid and to prevent the flow of hydraulic fluid from the cylinder back to the reservoir. The return side of the air cylinder is connected to the reservoir so that air under pressure is delivered to the reservoir to force hydraulic fluid from the reservoir into the high pressure cylinder as the high pressure piston is returned. It is therefore a principal object of this invention to provide a fluid pressure amplifier wherein the hydraulic fluid is self-filling at the end of each stroke to make up any hydraulic fluid which is lost by leakage.

It is a further object of the instant invention to provide an improved fluid pressure amplifier wherein the air pressure utilized to return an air piston is also utilized to force hydraulic fluid into the hydraulic system.

It is another object of the present invention to provide an improved cylinder construction wherein an elastic seal conforms to a tube end and a portion of a head.

It is a still further object of the herein-disclosed invention to provide an improved construction of a fluid pressure amplifier which is economical to manufacture and easy to maintain.

Other objects and uses of the present invention will become readily apparent to those skilled in the art upon a perusal of the following specification in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side-elevational view of a pressure system showing a hydraulically operated work holding device connected to a fluid pressure amplifier embodying the herein-disclosed invention;

FIG. 2 is an enlarged fragmentary cross-sectional view through a reservoir portion of the fluid amplifier shown in FIG. 1;

FIG. 3 is an enlarged cross-sectional view taken on line 3-3 of FIG. 2 showing the construction of an air flow path from the air cylinder to the reservoir and the construction of an air pressure control valve;

FIG. 4 is an enlarged fragmentary cross-sectional view of the fluid pressure amplifier shown in FIG. 1; and

FIG. 5 is an enlarged cross-sectional view taken on line 5-5 of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and especially to FIG. 1, FIG. 1 shows a fluid pressure amplifier generally indicated by numeral 10, which fluid pressure amplifier embodies the instant invention. The fluid pressure amplifier is connected to an air control valve 12 through pipes 14 and 16. Valve 12 is connected by an air line 18 to a conventional source of air under pressure, which source is not shown herein. The fluid pressure amplifier is connected to a hydraulic work holding device 20 by means of a conventional hydraulic line 22.

The construction of the fluid pressure amplifier 10 may be best seen in FIG. 4. The fluid pressure amplifier generally includes a large diameter air cylinder 24 connected to an oil pump or a small diameter, high pressure hydraulic cylinder 26. It may be seen that the longitudinal axis of cylinder 24 is aligned with the longitudinal axis of cylinder 26. A reservoir 28 is mounted on top of the air cylinder and surrounds the hydraulic cylinder 26 so that the reservoir is concentric with the cylinder 26.

The low pressure air cylinder 24 generally includes a base head 30, a tube 32 and a control head 34, which parts are held together by conventional tie rods 35. Mounted in the tube 32 is a piston 36 which is connected to a rod 38. The base head 30 includes an air inlet port 40 to which is connected the pipe 16. The head includes recess 42 in its center and a groove 44 into which is mounted the tube 32.

Tube 32 is not sealed to head by a conventional gasket but rather by a room temperature vulcanizing silicone rubber compound which conforms to the end of the tube and a portion of the head. It may be seen that there is no need to provide any additional fine machining of the tube end or the head other than cutting the groove in the head. In this instance, the elastic rubber compound is Silastic caulk manufactured and sold by Dow Corning Corporation of Midland, Mich. However, other manufacturers such as General Electric Company also manufacture and sell like compounds under their own brand names. When the tube is assembled to the head, a quantity of sealing compound in a high viscosity liquid form is layed in the groove. The tube is then placed in the groove and the sealing compound flows around the tube end and conforms to the groove and the tube end. The compound is allowed to cure so that the compound conforms in detail to the head and the tube end and becomes solid having an elastic rubberlike consistency. Any excess sealing compound may be cut away. It may be appreciated that the liquidity of the compound at application allows the material to flow into spaces so that any small errors in machining do not have any effect in the sealing between the head and the tube. Once the sealing compound is cured, the elasticity of the compound creates a seal which improves with sealing ability as fluid pressure is applied to the seal and the composition is held securely in position by its mechanical configuration since it conforms in detail to the groove and the tube end.

The rod 38 has a reduced section 46 with a threaded end 48. The piston 36 includes a piston plate 50 which is mounted on reduced section 46. A lower backup plate 52 is also mounted on the section 46 adjacent to piston plate 50. An upper backup plate 54 is mounted adjacent to piston plate 50 and in engagement with the rod 38. The piston plate 50 has a chamfer 56, and an O-ring 58 is mounted between the piston plate 50 and piston backup plate 54 and in engagement with the reduced section 46 to provide a seal between the parts. A conventional nut 60 is threadedly mounted on the threaded section 48 to hold the piston onto the rod 38. The piston is completed by a piston seal 62 which is molded integrally with the outer periphery of piston plate 50 and in sealing engagement with the interior of tube 32.

The control head 34 includes an air inlet 64 which is connected to pipe '14. The head includes a groove 66 into which is mounted the tube 32 and sealing compound 45 provides a seal therebetween. A reservoir groove 68 receives a portion of the reservoir 28. The control head includes a cylinder aperture 70 wherein the oil pump or high pressure cylinder 26 is mounted. Means is provided in the control head to allow hydraulic fluid to flow from the reservoir 28 to cylinder 26. The control head includes an axial aperture 72 which is connected to an oil control valve 74. The oil control valve is mounted in an oil valve aperture 76 in head 34, and the oil valve aperture terminates in a reduced oil port 77.

Oil control valve 74 includes a spring guide 78 which has a generally cylindrical head 80 with a pair of opposed flats 82, so that oil may flow past the spring guide. Formed integral with the head 80 is a spring shank 84, and a coil spring 86 is mounted on the spring shank. A conventional ball 88 is mounted in the aperture 76 in engagement with spring 86. The ball also engages a valve body 90. The valve body 90 includes a ball seat 92 at one end sealingly engageable with ball 88. A longitudinal port 94 extends through a portion of the valve body and opens into a lateral port 96. The valve body contains an enlarged oil groove 98 which communicates with both the axial aperture 72 and lateral port 96. The valve body also includes an inner oil ring groove 100 into which is positioned an O-ring 102 in sealing engagement with the valve body and the head 34. An outer groove 104 in the valve body has positioned therein an O-ring 106 also in sealing engagement with the valve body and head 34. An enlarged threaded portion 108, which also forms part of the valve body, is in threaded engagement with a female threaded section 110 of the oil valve aperture 76. A knob 112 is formed integral with the threaded portion to form a convenient means for turning the valve body to adjust the axial position of the valve body relative to the head to control the flow of hydraulic fluid through the valve. By moving the valve body axially until ball 88 is held firmly between ball seat 92 and spring shank 84, valve 74 is effectively closed so that no hydraulic fluid may flow to cylinder 26.

Looking now to FIG. 3, means connecting the low pressure cylinder with the hydraulic fluid reservoir and the construction of an air control valve 114 may be seen therein. The valve 114 controls the flow of air from the air cylinder 24 to the reservoir for forcing the hydraulic fluid into cylinder 26. The head 34 includes an air port 116, which opens into an air valve aperture 118. The air valve aperture 118 opens into a radial air port 120, which in turn opens into an inner air port 122. The inner air port 122 opens into a riser pipe 124 which extends up into reservoir 28. The valve 114 includes a body 126 with a stem 128 positioned in air valve aperture 118. The stem 128 includes a conical valve 130 which is seatable in radial air port 120. The valve body 126 also includes an enlarged threaded portion 132 which mates with an enlarged female threaded portion 134 of the air valve aperture 118. A head 136 with a cross-pin 138 fixed therein is fixed to body 126 to provide a convenient means grasping the extending portions of the valve for rotating the valve body and thereby adjusting the rate of flow of air through the radial air port 120. It is apparent that valve 114 may be selectively closed by seating conical valve 130 in radial air port 122.

Looking back to FIG. 4, it may be seen that the reservoir 28 includes a transparent cylindrical tube 140 which has one end sealingly mounted in groove 68 of the control head 34, and sealing compound 45 provides the necessary seal means therebetween as described above. A reservoir head 142 has a groove 144 which receives the upper end of tube 140, and sealing compound 45 provides a seal therebetween. The reservoir head 142 includes a filling aperture 146 which has a conventional plug 148 sealingly mounted therein. A relief valve 150 is mounted in a threaded relief valve aperture 152 in head 142. The relief valve 150 includes a relief valve body 154 having a port 156 communicating with a ball aperture 158 Which has a ported plug 160 mounted therein. The ported plug 160 includes a stud 162 which has a ball spring 164 positioned thereon and the ball spring engages a conventional ball 166 to hold the ball in engagement with the valve body 154 and thereby close the port 156.

The high pressure hydraulic cylinder includes a tube or sleeve 168 which has a flange 170 formed integral therewith, and the sleeve has one end positioned in aperture 70 with the flange 170 abutting the interior portion of head 34. The other end of sleeve 168 is positioned in an aperture 172 of head 142. The sleeve has an inner lock groove 174 which has mounted therein a lock ring 176 to hold the sleeve in position relative to control head 34. The sleeve has an outer lock groove 178 which has p0- sitioned therein a lock ring 180 to hold the head 142 relative to the sleeve and thereby, relative to the head 34. The sleeve also has an outer sealing groove 182 with an O-ring 184 positioned therein and in sealing engagement with the head 142 to form a seal therebetween. Sleeve 168 also includes a sealing groove 186 which has an O-ring 188 positioned therein to provide a seal between the sleeve and the head 34. A reservoir seal groove 190 is formed in the sleeve, and an O-ring 192 is positioned therein to form a second seal between the sleeve and head 34.

Sleeve or tube 168 is ported and grooved in order to allow oil to flow into the interior section of the sleeve. Sleeve 168 has an enlarged interior section 194 which has mounted in one end a conventional fitting 196. In the other end of section 194, there is a reduced high tolerance sliding portion 198 which mates with rod 38. An inner groove 200 is formed in portion 198, which groove communicates with a plurality of lateral ports 202. The lateral ports 202 communicate with an outer groove 204, a portion of which communicates with port 77. A seal groove 203 is formed in the interior of tube 163 with an O-ring 205 mounted therein to provide a seal between the tube and rod 38.

The cylinder 26 includes a piston 206 which is formed integral with rod 38. The piston 206 includes a radial oil port 208 and an axial oil port 210 which opens into the radial oil port and into the interior of sleeve 168.

The operation of the instant fluid pressure amplifier is quite simple inasmuch as it is only necessary to operate valve 12 to actuate and deactuate the hydraulic device 20. The air valve 12 is appropriately positioned so that air under pressure enters pipe 16 and flows through air inlet port 40, to apply pressure to one side of piston 36. As the piston moves toward head 34, the hydraulic fluid in the enlarged interior section 194 is pushed out by virtue of the displacement of the hydraulic fluid by piston 206 and rod 38. Thereby, the pressure of the hydraulic fluid is increased. When the appropriate pressure of the hydraulic device is attained, the pressure may be maintained by a continuous application of pressure to piston 36.

In order to relieve the hydraulic pressure from hydraulic device 20, valve 12 is manipulated so that the air on the side of the piston adjacent to head is dumped through the valve and air under pressure is delivered to the opposite side of piston 36; that is, in the space between piston 36 and head 34, thereby retracting piston 206 and rod 38 from space 194. It is important to note that the air under pressure is also delivered to the reservoir 28 when valve 114 is open inasmuch as the air flows through air port 116, air valve aperture 118, radial air port 120, inner air port 122, and riser pipe 124. The level of hydraulic fluid in the reservoir is maintained below the riser pipe so that the air does not flow through the hydraulic fluid to contaminate the fluid. In the event that the air pressure in the reservoir is too great, the air pressure is automatically relieved through the pressure relief valve 150 in view of the fact that excessive air pressure would displace the ball 166 against the force of spring 164 to relieve the pressure in the reservoir and thereby avoid overstressing of transparent tube 140.

The air pressure on the hydraulic fluid in the reservoir forces the hydraulic fluid to flow to cylinder 26 to replenish any leaked hydraulic fluid when valve 74 is opened. The hydraulic fluid under pressure flows through axial aperture 72 and then to enlarged oil groove 98, then to lateral port 96 and on into longitudinal port 94. The hydraulic fluid under pressure displaces ball 88 from seat 92, then flows past the flats 82 of head 80 and through port 77 to outer groove 204 of the sleeve. The hydraulic fluid flows in groove 204 and into lateral ports 202 of the sleeve and into inner groove 200. At this point, the hydraulic fluid in the reservoir is under pressure. However, it cannot flow inasmuch as it has no place to go. When the piston 36 reaches near the end of its return stroke, the radial oil port 208 of piston 206 is placed into communication with groove 200 so that the oil may flow through the axial oil port 210 and into the enlarged interior section 194. It is apparent that in the event that there should be any leakage of hydraulic fluid in any portion of the system, it is automatically replenished at the end of each stroke.

The construction of the instant fluid pressure amplifier is such that the amount of oil flow from the reservoir may be simply and conveniently controlled by an adjustment of the oil control valve 74. Also, the pressure which is applied to the oil in the reservoir may be controlled by an adjustment of air control valve 114. Furthermore, there is no danger of an undue amount of pressure being placed on the fluid in view of the fact that the oil reservoir contains the relief valve 150.

The subject fluid pressure amplifier allows the hydraulic fluid system to be purged simply and conveniently. The system is filled with hydraulic fluid and a bleed part at the top of the system as in the top of device 20 is opened. Air is applied to the return side of piston 36 while valves 74 and 114 are opened so that hydraulic fluid is forced through the system until clear hydraulic fluid flows out of the bleed part. The bleed part is closed and valves 74 and 114 are appropriately adjusted and the system is in condition for normal operation.

It may be appreciated that the instant fluid pressure amplifier may be filled while the device is in operation. It is only necessary to remove the plug 148 and pour additional hydraulic fluid into the reservoir through aperture 146. It is readily apparent that the plug should not be removed when the oil in the reservoir is under pressure. It is also readily apparent that the instant fluid pressure amplifier may be used over protracted periods of time, even though there may be leaks in the hydraulic system, without stopping the ordinary operation of the device. The fluid may be added as needed by a very simple operation, and if the hydraulic fluid leaks out through the hydraulic device 20 or through leaks in the line 22, the amount of lost hydraulic fluid is replaced at the end of each stroke, so that at no time is there any substantial partial vacuum in the line which would suck in air to contaminate the hydraulic system.

From the foregoing description, it may be seen that the instant device is economical to manufacture and simple to maintain. The maintenance of an appropriate level of hydraulic fluid in the reservoir is facilitated by virtue of the fact that the reservoir has a transparent outer wall so that the level of the hydraulic fluid may be readily and conveniently observed.

Although a specific embodiment of the instant invention has been shown and described in detail above, it is to be expressly understood that those skilled in the art may make various modifications and changes without departing from the spirit and scope of the invention. It is to be understood that the subject invention is limited only by the appended claims.

What is claimed is:

1. A fluid pressure amplifier comprising, in combination; a large diameter, low pressure pneumatic cylinder; said low pressure cylinder including a reciprocally mounted piston; a rod connected to said piston; a small diameter, high pressure hydraulic cylinder connected to the low pressure pneumatic cylinder; said high pressure cylinder including a reciprocally mounted high pressure piston connected to the rod; a hydraulic fluid reservoir; means connecting the fluid reservoir with the high pressure cylinder; and a valve for controlling the flow of hydraulic fluid from the fluid reservoir to the high pressure cylinder and preventing the flow of hydraulic fluid from the high pressure cylinder to the fluid reservoir.

2. A fluid pressure amplifier as defined in claim 1, wherein the low pressure pneumatic cylinder and the high pressure hydraulic cylinder have a common head, the longitudinal axis of the low pressure pneumatic cylinder is aligned with the longitudinal axis of the high pressure hydraulic cylinder, the hydraulic fluid reservoir is concentric with the high pressure hydraulic cylinder and has a common longitudinal axis with the high pressure hydraulic cylinder, and one end of the hydraulic reservoir is defined by the common head between the low pressure pneumatic cylinder and the high pressure hydraulic cylinder.

3. A fluid pressure amplifier as defined in claim 2, wherein the hydraulic fluid reservoir includes a cylindrical transparent wall defining an outer surface of the reservoir.

4. A fluid pressure amplifier as defined in claim 2, wherein the high pressure piston is formed integral with the rod and includes a hydraulic fluid flow path from the face of the piston to the side of the piston, said high pressure hydraulic cylinder includes a groove which communicates with the hydraulic fluid flow path when the high pressure piston is near the end of its return stroke, and said groove is connected to the valve.

5. A fluid pressure amplifier as defined in claim 1 including means connecting the low pressure pneumatic cylinder with the hydraulic fluid reservoir to provide a flow path for a pneumatic fluid from the low pressure pneumatic cylinder to the hydraulic fluid reservoir for forcing by fluid pressure hydraulic fluid from the fluid reservoir into the high pressure cylinder.

6. A fluid pressure amplifier as defined in claim 5, including a pressure relief valve in the fluid reservoir.

7. A fluid pressure amplifier a defined in claim 1, wherein the low pressure pneumatic cylinder includes a head having a circular groove formed in one side thereof, a cylindrical tube mounted in said groove, and an elastic composition positioned in said groove and conforming to the groove in the head and the tube to form an elastic seal therebetween.

8. A fluid pressure amplifier as defined in claim 1, wherein the high pressure piston is formed integral with the rod and includes a hydraulic fluid flow path from the face of the piston to the side of the piston, said high pressure hydraulic cylinder includes a groove which communicates with the hydraulic fluid flow path when the high pressure piston is near the end of its return stroke, said groove is connected to the valve, and including means connecting the low pressure cylinder with the fluid reservoir providing a flow path for a fluid from the low pressure cylinder for forcing hydraulic fluid from the fluid reservoir into the high pressure cylinder through the high pressure piston.

9. A fluid pressure amplifier as defined in claim 1, wherein the loW pressure pneumatic cylinder and the high pressure hydraulic cylinder have a common head, and the longitudinal axis of the low pressure pneumatic cylinder is aligned with the longitudinal axis of the high pressure hydraulic cylinder.

10. A fluid pressure amplifier as defined in claim 1, wherein the high pressure piston is formed integral with the rod and includes a hydraulic fluid flow path from the face of the piston to the side of the piston, said high pressure hydraulic cylinder includes a groove which communicates with the hydraulic fluid flow path when the high pressure piston is near the end of its return stroke, r

and said groove is connected to the valve.

11. In a cylinder construction having a first head, a second head, and a tube between said heads, a piston reciprocally mounted within said tube between said heads, and a rod connected to the piston and extending through one of said heads, the improvement comprising, a groove in one of said heads having one end of the tube positioned in the groove, and a room temperature curing elastic composition positioned in and conforming to a portion of the groove and to the end of the tube to form an elastic seal between the tube and the head.

12. A fluid pressure amplifier comprising, in combination, a base head for a low pressure pneumatic cylinder, a cylindrical tube having one end sealingly connected to the base head, a control head sealingly connected to the other end of the tube, a low pressure pneumatic piston slidably mounted in the tube, a rod connected to the piston and extendable through the control head, a high pressure hydraulic tube sealingly mounted on the control head and having its longitudinal axis aligned with the longitudinal axis of the first-mentioned tube, means connected to the other end of the high pressure hydraulic tube for closing the end of the tube, a transparent cylindrical reservoir tube sealingly mounted on the control head and concentric with the high pressure tube, a reservoir head sealingly mounted in engagement with the reservoir tube and the high pressure tube, a relief valve mounted in the reservoir head, a high pressure piston formed integral with the rod and slidably mounted in the high pressure tube, a flow path in the high pressure piston from the face of the piston to the side wall of the piston, a groove in the interior surface of the high pressure tube, a port extending through the high pressure tube and communicating with the groove, a flow path through the control head from the fluid reservoir to the port in the high pressure tube, a valve mounted in the flow path to regulate the flow of hydraulic fluid from the fluid reservoir to the high pressure cylinder and to restrict the flow of hydraulic fluid from the high pressure cylinder back to the fluid reservoir, a second fluid flow path in the control head from the interior of the low pressure tube to the interior of the fluid reservoir, a riser mounted within the reservoir tube and connected to the second fluid flow path in the control head, and a second valve mounted in the second fluid flow path for controlling the flow of fluid from the interior of the low pressure tube to the interior of the reservoir tube, whereby pneumatic fluid under pressure in the interior of the low pressure tube flows into the interior of the reservoir tube to force hydraulic fluid through the first-mentioned fluid flow path to the interior of the high pressure cylinder through the piston.

References Cited UNITED STATES PATENTS 2,737,157 3/1956 Hefner et al 92169 XR 2,842,284 7/1958 Flick 92-169 XR 3,122,063 2/1964 Chorkey 92-169 XR 3,382,770 5/1968 Berninger et al. 92--16 5 XR 3,425,219 2/1969 Oliver et al. 3,200,596 8/1965 Olson et al.

FOREIGN PATENTS 114,546 1/1942 Australia.

662,397 12/1951 Great Britain. 1,021,307 3/ 1966 Great Britain.

MARTIN P. SCHWADRON, Primary Examiner R. R. BUNEVICH, Assistant Examiner US. 01. X.R. 60-546; 92-165, 169

Po-105O Patent No.

Dated November 24 1970 Inventor(s) John T. Ellis Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, Line 69 "hydaulic" should be hydraulic-- Column 6, Line 69 after "hydraulic insert fluid- Column 7, Line 18, "a" should be as- .a.%=-iifi AND EAKEB Febuary 2, 1971 (SEAL) Attest:

EdMM-Fletchmln WILLIAM R- SGHUYLE Gonnissiom 01' Pa AneatingOfficcr 

